Magnetic Shielding Effect Research Articles

Feasibility Study of High-Efficiency Cooling of High-Temperature Superconducting Coils by Magnetic Refrigeration

As a high-efficiency cooling technology for high-temperature superconducting coils, we have begun research and development to examine the feasibility of a cooling assist technology that maintains a cryogenic state by combining the magnetic force generated by the superconducting coil with magnetic refrigeration technology. Magnetic refrigeration requires the magneto caloric material to change the magnetic field. In many cases, the magnetic field change is obtained by moving the magnetic source, but moving the superconducting coil is not a good idea. Although it is possible to generate a change in the magnetic field by turning on and off the power supply of the high-temperature superconducting coil, it is unlikely to be established as a system that assists cooling of the superconducting coil because the coil generates heat due to AC loss. Therefore, it was considered that the magnetic field change can be obtained if the magnetic force generated from the superconducting coil can be controlled by the magnetic shield. As a verification of the principle, it was clarified experimentally that a magnetic field change can be obtained by repeatedly inserting and removing the magnetic shield into and from the gap between the magnetic field generation source and the magneto caloric material, and the temperature change can be extracted by the magneto caloric effect. In the experiment, the temperature change obtained when a magnetic shield was inserted into the air gap was measured by a simple test device using an iron-based magneto caloric material having high magneto caloric effect performance at room temperature and a permanent magnet. The principle verification confirmation test was performed using several types of magnetic shielding materials such as Permalloy bulks and the electrical steel sheets. In addition, numerical analysis is performed on the magnetic shielding effect, and the shielding effect is improved by increasing the thickness of the shielding material and the possibility of using high temperature superconductors as magnetic shielding materials were also analyzed. In this study, we report the possibility of cooling the high-temperature superconducting coil with high efficiency by combining the magnetic field created by the superconducting coil and magnetic refrigeration.

Prediction of magnetic shield plate performance using permeability in alternating micromagnetic fields

Magnetoencephalographs (MEGs) are highly sensitive to magnetic noises, and thus, a high performance magnetically shielded room (MSR) is essential. The shielding effect of a novel MSR should predicted to verify if it satisfies the required specifications of the MEG at the design stage. Therefore, an accurate prediction method based on the properties of shielding materials and shape of the MSR is necessary. We focused on the initial permeability μi of mu-metals which are generally used for MEGs; further, we proposed an estimation method for μi and a prediction method for the shielding effect using μi. To verify the prediction accuracy, we estimated μi of mu-metals and predicted the shielding effect of a plate, as simple examples, and compared the obtained result with experimental results. The comparison indicated that the prediction method can predict the shielding effect within approximate deviation of 8.2% for the plate even in a small magnetic field fluctuation region with a magnetic field as low as ΔH = 0.001 A/m. This result provided an important step necessary for predicting the magnetic shield effect of MSRs.

Significant enhancement of magnetic shielding effect by using the composite metamaterial composed of mu-near-zero media and ferrite

The magnetic shield plays an important role in magnetic near-field control. However, the requirements of efficiency, ultra thinness, lightness and cheapness are still the challenges. Here, we firstly propose a composite metamaterial in which the mu-near-zero media is covered with a ferrite slab. We verify that this structure can enhance the shielding effectiveness (SE) in a small area. Furthermore, we optimize the magnetic path by changing the bulk ferrite slab into a patterned slab. In this way, significant SE enhancement can be achieved in a large area. Experimental results show that the maximum SE of the composite metamaterial with a patterned ferrite is 20.56 dB, which is nearly 19 dB higher than that of a single ferrite slab with the same thickness of the composite metamaterial. The results on the composite metamaterial would be very useful in the applications involving magnetic shielding.

Development of High-Order Functions Using (-)-Epigallocatechin-3-O-gallate in Water.

The high-order functions of molecular capture and chiral recognition of tea gallated catechins (-)-epigallocatechin-3-O-gallate (EGCg) in water were investigated. A solution of equimolar amounts of a variety of heterocyclic compounds and EGCg in water afforded adhesive precipitates containing the heterocyclic compounds and EGCg at a molar ratio of 1 : 1, based on the integrated value of NMR proton signals. The molecular capture abilities of a variety of heterocyclic compounds using EGCg from the aqueous solutions were evaluated with the ratios of the heterocyclic compounds included in the precipitates of EGCg complex to the total heterocyclic compounds used. In the 1H-NMR spectrum of a solution containing cyclo(L-Pro-Gly), cyclo(D-Pro-Gly), and EGCg in a D2O solution, a difference in the chemical shift of the 1H-NMR signal for some protons of the Pro residue was observed. Judging from the crystal structures of the 2 : 2 EGCg complexes of cyclo(L-Pro-Gly), cyclo(D-Pro-Gly), the difference in the chemical shift derived mainly from a magnetic anisotropic shielding effect by the ring current from the B ring of EGCg.In the 1H-NMR spectrum of a solution containing the pharmaceuticals racemic (R,S)-propranolol, (R,S)-diprophylline, (R,S)-proxyphylline and EGCg in D2O, splitting of the 1H-NMR signals of the pharmaceuticals was observed. It was suggested that the pharmaceuticals formed diastereomers of EGCg complexes, as a result chirality of the pharmaceuticals was recognized by EGCg in the D2O solution.

Closed-Form LF Magnetic Shielding Effectiveness of Thin Planar Screens in Coplanar Loops Configuration

In this article, the low-frequency magnetic shielding effectiveness of a planar screen with magnetic and conductive properties in a coplanar-loops configuration (as required in the IEEE Standard 299) is evaluated through a new closed-form formula under the thin-sheet and small-loop approximations. The formulation clearly shows the separate contribution of the permeability and the conductivity of the screen to the shielding performance. The results obtained with the proposed closed-form formulas are compared with the exact ones derived through numerical integrations to assess the relevant accuracy and limits of validity.

Low-frequency magnetic field shielding effect of artificial joint-free REBCO coils

The screening current induced in superconductors can passively shield external magnetic fields and hence provide a noise free environment for precision sensors and instruments. This paper presents a novel design employing artificial joint-free REBCO (REBa2Cu3O7-x, RE: rare earths) coils which can economically extend the field shielding space for larger instruments, e.g. clinical equipment. We compared the shielding factors of single, double and multi-coils, and confirmed a coil with Helmholtz construction as the optimal architecture. Due to the zero resistance of the joint-free REBCO coils, the shielding effectiveness reaches 80 dB at the center of coils, shielding 99.99% of the external magnetic field of 10 μT at 1 × 10−5 Hz, and 40 dB (99%) in a greater spherical space of 40 mm in diameter. Additionally, the shielding effectiveness does not decrease in the external magnetic field of 1 nT. Such a low frequency magnetic shielding effect implies promising applications for the present work, such as preventing interference magnetic fields from precision instruments, which generally require field sensitivity as low as the fT · Hz−1/2 range.

Study of the Effectiveness of Magnetic Shielding for Compact Power Transformers Used on Mobile Applications

This paper presents the performance analysis of a new type of leakage flux collector, designed to act as magnetic shielding in compact power transformers for mobile applications. The analysis was made through 3-D finite-element computer program for modeling and simulating the operation of a 33.3 MVA, 69.3/13.8 kV three-phase compact transformer with and without adoption of the proposed leakage flux collector. The results show that due to its shape and its position in the core transformer this type of leakage flux collector efficiently mitigates the undesirable stray losses and hot spots in some key structural parts of the compact transformers, such as tank and beams.

Magnetization influence analysis of the casing and drill pipe in shale gas dual horizontal well Rotating Magnet Ranging System drilling process

AbstractRotating Magnet Ranging System (RMRS) is one of the core guiding technologies for shale gas extraction, and its magnetic measurement data will inevitably be affected by the downhole magnetic objects in the target magnetic field. The casing and drill pipe, which are apt to be magnetized by the magnetic sub, are major influencing factors of the measurement results. In order to study the influence comprehensively, a dual horizontal well RMRS drilling model is established. Based on static magnetic dipole theory, the magnetic field distribution equation of the low‐rotational magnetic sub is deduced and characterized. Firstly, the casing and drill pipe were segmented into ring, layer, and block volume elements. Then according to the dynamic magnetic dipole field distribution equation, the magnetic field strength of the magnetic source at the volume element (equivalent magnetic dipole) and the sensor was calculated, as well as the magnetic strength of independent magnetization field and superposition magnetization field of casing and drill pipe at the sensor position. Finally, the effectiveness of the numerical method results was verified by outdoor experiments, and the shielding effect of the static magnetic shielding on the external magnetic field of casing was preliminarily analyzed. The research results indicate that the magnetic sub has a strong magnetization effect on the casing and drill pipe. The magnetization field of the casing is about 2.39 times stronger than that of the drill pipe, and they will seriously affect the sensor measurement data. When the well spacing is small, the magnetization field waveform will be distorted. With the increase of the well spacing d, the waveform gradually changes sinusoidally, the fluctuation period of the magnetization field also gradually becomes twice (d > 1.5 m) that of the magnetic source, and the peak value of the magnetization field decreases exponentially. A preliminary analysis of the magnetic shielding of casing revealed that the magnetic shielding would cause great attenuation to the strength of the magnetic source. The numerical simulation proposed in this paper provides a theoretical basis for the error analysis of RMRS, which is of great significance for measurement correction and accuracy improvement.

Analytical Evaluation of the Low-Frequency Magnetic Shielding of Thin Planar Magnetic and Conductive Screens

A recent analytical formulation for the low-frequency magnetic shielding effectiveness of a thin metal screen against a circular loop source is extended to the case of a screen exhibiting both magnetic and conductive properties. The presence of magnetic properties introduces a series impedance in the equivalent network of the structure, in addition to the shunt admittance associated with the screen conductivity. However, the fields scattered by the two elements do not interact and hence can be treated independently; furthermore, the series impedance gives rise to integrals akin to those stemming from the shunt admittance. A generalized analytical formulation for a combined magnetic and conductive screen is thus obtained, that is favorably compared with both classical approximate formulations and exact results.

Low Frequency Magnetic Shielding Effectiveness of a Conducting Plate With Periodic Apertures

This article focuses on the shielding effectiveness (SE) prediction of the periodic aperture array on an infinite PEC plate against the low frequency (≤1 MHz) magnetic field resulting from a current loop parallel to the plate. Two different models of the penetration field through the plate are presented. From the two models, the same simplified expression for the field on the central axis is derived. The SE of a 1000 mm × 1000 mm aluminum plate with 2500 apertures against the magnetic field from a current loop is measured. The results show that the theoretical results are in good agreement with the measurement if the frequency is higher than a critical frequency. Above the critical frequency, penetration from the apertures is primary factor for field leakage, and the SE is constant with the increasing frequency. When the frequency is lower than the critical frequency, penetration from the aluminum is primary channel for field leakage, and hence the SE reduces with the decreasing frequency. In this case, the upper limit of the SE does not exceed the SE of the corresponding solid plate without apertures.

Magnetic shielding of a thin Al/steel/Al composite

PurposeThis paper aims to investigate the efficiency of a laminated composite for shielding applications. The solution has to be efficient not only for the shield against static magnetic fields but also “for low-frequency ones, in order to be well-suited for applications with electromagnetic perturbations in the frequency range DC to 100 kHz.”Design/methodology/approachThe composite constituted of a steel sheet taken in a sandwich between two aluminum (Al) sheets is produced by cold roll bonding. A good adherence between Al and steel sheets, ensuring a good mechanical resistance, is obtained with a specific process. A previous study has shown that the optimal trade-off between adherence and magnetic shielding effectiveness (SEH) is obtained with a 230 µm composite produced with an initial thickness of Al and steel sheets, respectively, of 250 and 100 µm. In this paper, the 230 µm Al/steel/Al composite is used in three applications modelized by two-dimensional numerical simulations. To obtain reasonable computation time for the simulations, a homogenization method is applied to the composite. Studied applications are a cylindrical box containing a coil, a square box under an external magnetic field and a high voltage cable.FindingsIn each application, SEH is calculated at low frequency and different materials (Al/steel/Al, Al, steel and copper) are compared. It is observed that, in each application, the composite presents higher SEH at equal mass, especially for frequencies between 5 and 100 kHz.Originality/valueThe proposed approach, from the material point of view to the system consideration, shows that the thin bimetallic composite is an innovative and promising solution for magnetic shielding in the case of applications with both DC and low-frequency perturbations.

Analysis of Magnetic Shielding Effect on an RFID Coil Antenna in Metallic Environments With a Ferrite Toroid

Deleterious effects of the metallic environments on a radio frequency identification (RFID) antenna are often alleviated by the magnetic shielding. This article presents a novel model to study quantitatively the magnetic shielding effect on an RFID coil antenna in metallic environments with a ferrite toroid. From the proposed model, the magnetic field intensity within the antenna is derived, and the computational results are in good agreement with those from the numerical simulations. Then, the optimal geometrical parameters of the ferrite toroid for proper shielding are investigated, and the shielding effect on an RFID solenoid coil antenna against the metal is discussed. Finally, an experiment has been carried out and the results show that the shielding with the ferrite toroid can alleviate the deleterious effects of the metals almost completely.

Investigation on ion behavior in magnetically shielded and unshielded Hall thrusters by laser-induced fluorescence

Non-intrusive characterization of the ion velocity distribution functions at several points of interest in 600 W magnetically shielded MSHT-600 and unshielded USHT-600 Hall thrusters plume by laser-induced fluorescence was conducted. Several visual clues supporting the magnetic shielding effect of MSHT-600 were presented. The measured ion axial velocity distribution functions show that the ion axial velocity is higher and observed to reach the maximum at nearer location to the exit plane on the centerline in the magnetically shielded Hall thruster than that in the unshielded one under the same operating conditions but uniformly distributed in the radial direction when ignoring the slower population for both thrusters. These results are in accordance with the higher specific impulse measured in several other shielded Hall thrusters. Moreover, the ion axial velocity on the centerline is higher than the average axial velocity at other radial locations for the same axial distance downstream of the exit plane in USHT-600, while the higher plume divergence or the inner pole erosion causes the velocity on the centerline to decrease in MSHT-600. The downstream shift of the accelerating potential and electric field distribution are also the typical features in magnetically shielded Hall thrusters as reported in other studies. Finally, the xenon ion velocity vector fields show that the ion population starts to meet and diverge further downstream of the exit plane in MSHT-600 than that in USHT-600, which may be associated with the difference of the plume divergence.

Improved Magnetic Circuit Model for Magnetic Shielding Effectiveness in Rogowski Coil

The magnetic circuit approach is commonly used as a powerful analysis and design tool for magnetic devices because of its computational simplicity and comparable accuracy. Currently, magnetic circuit solutions for magnetic shielding effectiveness assume a rectangular shell structure of shielding under vertical external magnetic fields, leading to inaccuracies in parametric analysis. In this article, an improved magnetic circuit model is proposed by considering the hollow cylindrical structure of shielding to investigate magnetic shielding effectiveness in Rogowski coils. The proposed model is verified by simulation studies based on the finite-element method (FEM) for a wide range of design parameters. It is shown that magnetic shielding effectiveness of magnetic circuit models has no more than 27% error for horizontal air gaps and 17% for vertical air gaps when the shielding thicknesses and the shielding distances from non-magnetic former are varied from 5 to 30 mm. The proposed magnetic circuit approach has also been confirmed by magnetic shielding of a hollow toroidal structure. It is found that the maximum percentage error in the magnetic shielding effectiveness does not exceed 18% for the same parameter range. The method is also validated for the changes in air gaps, permeability of shielding materials, and the major radius of the non-magnetic former.

Experiment on determination of ethanol chemical shift and concentration of ethanol solution based on nuclear magnetic resonance instrument

In this designing experiment, a nuclear magnetic resonance instrument was used to study the chemical shift properties of ethanol based on the principle of magnetic shielding effect. At the same time, the nuclear magnetic resonance method was used to study the transverse relaxation time and signal strength of ethanol aqueous solution in the range of 5%to 40%. The relationship between different mass fraction of ethanol-aqueous solution and nuclear magnetic resonance signal intensity, relaxation time and solution concentration were analysed. According to the results, due to the limitation of experimental instruments, no regular changes were observed. The results show that the addition of copper sulphate can increase the ethanol content and the effect of the ethanol content on the lateral relaxation time: the ethanol content varies between 5% and 40%, and the lateral relaxation time changes from 8.42ms to 40.35ms.According to the experimental results, the empirical formulas of the concentration and lateral relaxation time of ethanol aqueous solution with fixed amount of copper sulphate were fitted. Using this relationship, the NMR measurement of the concentration of ethanol-water solution can be achieved, which provides a new method for the convenient and accurate measurement of the concentration of ethanol solution.

Research on the influence of screw spacing on magnetic shielding effectiveness of a shielding cabin

Large shields are usually formed by splicing small pieces of metal, resulting in gaps that affect the shielding effectiveness of the shield. Affected by the screw fixed spacing, the size of the slits will also be changed. Since it is difficult to deduce the influence of fixed spacing on shielding effectiveness by theoretical formula or software simulation, we built a 2m*2m*2m shielding cabin model and explored the influence of fixed spacing on shielding effectiveness by changing the fixed spacing of screws. During measurement, the selected frequency range was 0.25-1000MHz. In the selected frequency range, for different frequencies, different antennas were used and a total of 22 frequency points were selected for measurement. The results show that the smaller the screw spacing, the greater the shielding effectiveness. When the screw spacing is reduced by half, the shielding effectiveness increases by about 6-8dB, especially at low frequency. When screw spacing is 0.25m, the maximum shielding effectiveness is about 44dB, the minimum is about 25dB, and the average shielding effectiveness is about 35dB. In addition, the polarization mode and antenna position have little influence on the results. So it can be used as a guide and reference for the design of large shielding body in the future.

Discussion on Anisotropic Magnetic Shielding Effectiveness of Shielded Package Analyzed by Magnetic Circuit Calculation

Discussion on Anisotropic Magnetic Shielding Effectiveness of Shielded Package Analyzed by Magnetic Circuit Calculation

Analytic Magnetic Shielding Effectiveness of Multiple Long Slots on a Metal Plate Using Rectangular Loops

This article proposes an analytical formulation to calculate the magnetic near-field shielding effectiveness (SE) of a metal plate with multiple long slots in the low frequency range below 10 MHz. Mutual inductances of two rectangular loop antennas in the presence and absence of the metal plate with slots are analytically derived. Then, the magnetic SE is obtained by the ratio of two analytic mutual inductances. In addition, an analytical SE formulation based on the transmission line model is used to consider the diffusion effect caused by a low conductivity of the metal plate. The total magnetic SE is finally determined by choosing the minimum SE between two analytic results due to the slot and diffusion effects. For validation, the results obtained by the proposed method are compared with the numerical results of full-wave simulation, and good agreement is achieved.

Magnetic Shielding of Planar Metallic Screens: A New Analytical Closed-Form Solution

The magnetic shielding effectiveness of a planar metallic screen of infinite extent against a circular loop field source is analytically evaluated in a new closed-form formula under the thin sheet and small-loop approximations. The results obtained with the proposed formulation are compared with the exact ones derived numerically and with those obtained through classical approximate formulations. It is thus shown that the proposed formula is the most accurate closed-form expression proposed so far and the frequency range where a percentage relative error less than $\text{1}\%$ is obtained is clearly identified.

Effect of Vertical Metal Plate on Transfer Efficiency of the Wireless Power Transfer System

Power transfer efficiency is an important issue in wireless power transfer (WPT). In actual applications, the WPT system may be exposed to a complex electromagnetic environment. The metal which is inevitably or accidentally close to the system will impact the power transfer efficiency. Most previous research has aimed at the effect of the metallic sheet paralleled to the resonant coil. This paper focuses on the effect of the metallic plate perpendicular to the resonant coils. Firstly, based on the theoretical analysis, a simulation model is setup using COMSOL Multiphysics. The efficiencies of the double-coils magnetic resonant WPT system with the presence of the parallel and vertical aluminum plate are studied comparatively. Efficiency improvement is observed with the vertical plate while the reduction appeared with the presence of the parallel plate. The vertical metallic plate has shown a magnetic field shielding effect according to the magnetic field distribution. It can reduce the radial magnetic field and enhance the axial magnetic field. Then, the effects of the position and size of the vertical plate are studied. It is found that the transfer efficiency has a preferable improvement when the vertical aluminum plate with a larger size is placed between the resonant coils and near outer edge of the windings. Finally, the experiment is carried out to verify the effect of the vertical aluminum plate on the WPT system.